1. Field of the Invention
The present invention relates to a circularly polarizing radar transponder capable of being adapted to any of a circularly polarizing radar, a horizontally polarizing radar and a vertically polarizing radar, as well as a lifesaving apparatus using the same.
2. Description of the Background Art
As a radar transponder which has heretofore been used in lifesaving apparatus, there is known one shown in FIG. 7 by way of example.
In the drawing, reference numeral 11 indicates a slot type horizontally polarizing antenna unit common to transmission and reception, which is capable of transmitting and receiving a radio wave corresponding to a horizontally polarized wave. Reference numeral 2 indicates a receiver unit for amplifying and detecting the radio wave received by the slot type horizontally polarizing antenna unit 11 to thereby generate a trigger signal therefrom. Reference numeral 3 indicates a transmitter unit for generating a plurality of sweep signals lying in the same frequency band as that of the radar wave, based on the trigger signal sent from the receiver unit 2. Reference numeral 4 indicates a battery unit for supplying power to the receiver unit 2 and the transmitter unit 3. Reference numeral 5 indicates a case with a radome, which accommodates the slot type horizontally polarizing antenna unit 11, the receiver unit 2, the transmitter unit 3 and the battery unit 4 therein.
The operation of the radar transponder will next be explained.
A radio wave received by the slot type horizontally polarizing antenna unit 11 is amplified and detected by the receiver unit 2, followed by supply to the transmitter unit 3 as a trigger signal indicative of the incoming of the radar wave. The transmitter unit 3 generates a plurality of sweep signals lying within the same frequency band as that of the radar wave, based on the trigger signal sent from the receiver unit 2 and sends these sweep signals to the slot type horizontally polarizing antenna unit 11. The slot type horizontally polarizing antenna unit 11 radiates the plurality of sweep signals sent from the transmitter unit 3 into space as a horizontally polarized electromagnetic wave. The electromagnetic-wave radiated into space is principally received by, for example, a horizontally polarizing radar (not shown) having a required band and thereby recognized as a distress signal.
The conventional horizontally polarizing radar transponder has a problem in that since it is constructed as described above, a polarization loss is so high with respect to the vertically polarizing radar and it cannot cope with a vertically polarizing radar.
The present invention has been conceived to solve the previouslyxe2x80x94mentioned problems. It is therefore the first object of the present invention to provide a circularly polarizing radar transponder enabling to communicate even with a vertically polarizing radar as well as with a circularly polarizing radar and a horizontally polarizing radar while predetermined antenna performance (coverage or covering area, gain, etc.) is being maintained by using a circularly polarizing antenna as an alternative to a horizontally polarizing antenna.
Further, it is the second object to provide a lifesaving apparatus using the circularly polarizing radar transponder.
The above objects of the present invention are achieved by a circularly polarizing radar transponder described below. The transponder includes a circularly polarizing antenna unit for receiving all of a circularly polarized wave, a vertically polarized wave and a horizontally polarized wave therein. A receiver unit is connected to the circularly polarizing antenna unit. A transmitter unit is provided for generating a plurality of pulses upon recognizing a radio wave received by the receiver unit as a trigger. The transponder also includes a battery for supplying power to the receiver unit and the transmitter unit.
The above objects of the present invention are achieved by a lifesaving apparatus which is provided with the circularly polarizing radar transponder described above.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.